Largest number formed from an array

//#include <iostream>
#include<bits/stdc++.h>
using namespace std;

bool comparator(string first,string second)
{
    string one = first+second;
    string two = second+first;
    
    int i=0;
    while(one[i] && two[i])
    {
        if(one[i]>two[i])
            return true;
        else if(one[i]<two[i])
            return false;
        ++i;
    }
    
    return false;
}

int main() {
	//code
	int tc;
	cin>>tc;
	while(tc--)
	{
	   int len;
	   vector<string> arr;
	   
	   //Take Array inputs
	   int i;
	   string temp;
	   cin>>len;
	   for(i=0;i<len;++i)
	   {
	       cin>>temp;
	       arr.push_back(temp);
	   }
	   
	   sort(arr.begin(),arr.end(),comparator);
	    
	   for(i=0;i<len;++i)
	       cout<<arr[i]<<" ";
	   cout<<"\n";
	}
	return 0;
}

class Solution {
public:
string largestNumber(vector& nums) {
vectornums1;
string st="";
for(int i=0;i<nums.size();i++){
nums1.push_back(to_string(nums[i]));
}
for(int i=0;i<nums1.size();i++){
for(int j=i+1;j<nums1.size();j++){
if(nums1[i]+nums1[j]<nums1[j]+nums1[i])
swap(nums1[i],nums1[j]);
}
}
for(auto p:nums1){
st+=p;
}
return (st[0]=='0'?"0":st);
}
};